port of redo-c to BetterC

[jfondren]

On Wednesday, 9 June 2021 at 21:45:33 UTC, aquaratixc wrote:
> 1. In the original implementation, there are places where the 
> openat function is used (dir_fd, target, O_RDONLY | 
> O_DIRECTORY); and I couldn't find a replacement. Are there any 
> options where you can get it?
> 2. Similarly, the dprintf function was not found, which, as I 
> understand it, is a non-standard extension. Is there a way to 
> add this?

In general you can just use the C functions directly, with 
reference to system
manpages, prior interfaces in D repositories (dmd+phobos+druntime 
are good
repos to have around), https://dlang.org/spec/interfaceToC.html , 
and (until
ImportC lands) your system's headers for the right magic numbers.

```d
extern(C) nothrow @nogc int dprintf(int fd, scope const char* 
format, ...);
extern(C) nothrow @nogc int openat(int dirfd, scope const char 
*pathname, int flags);
extern(C) nothrow @nogc int openat(int dirfd, scope const char 
*pathname, int flags, int mode);
extern(C) nothrow @nogc int close(int fd);
import core.sys.posix.fcntl : AT_FDCWD, O_RDONLY;
enum O_DIRECTORY = 0x10000;
import std.stdio : File, write;

void main() {
     int dir, file;
     if (-1 != (dir = openat(AT_FDCWD, "test", O_DIRECTORY | 
O_RDONLY))) {
         scope(exit) close(dir);
         if (-1 != (file = openat(dir, "x", O_RDONLY))) {
             File f;
             f.fdopen(file, "r");
             write("test/x contained: ", f.readln);
         }
     }
}
```